1. Field of the Invention
This invention relates to turbine cooling air systems for use in gas turbine engines.
2. Summary of the Prior Art
As turbine inlet temperatures have been increased in order to improve the efficiency of gas turbine engines, it has become necessary to provide cooling air to the turbine blades and vanes in order to limit the temperatures of those components to levels that can be withstood by the materials used to make those components. At higher operating temperature conditions, such as take off when the engines are used to power airplanes, the amount of cooling air that is required is relatively high. In contrast, during lower temperature operating conditions, such as at idle, there is relatively little, if any, cooling air required for the turbine components. In spite of these very different operating conditions, for reasons of simplicity and safety, it has not generally been considered desirable to modulate the flow of cooling air to the turbine components. As a result, since the engine must be designed so as to provide the amount of cooling airflow required for maximum temperature operation, an excessive amount of cooling air is provided during other operating conditions which tends to reduce the efficiency of the engine during those operating periods. The excess flow at these conditions is wasteful resulting in poor performance and higher fuel consumption than would be the case if this flow could be reduced to the minimum amount required for each particular operating condition.
In response to this efficiency problem, various concepts have been proposed and studied for controlling or modulating the turbine cooling flow thus eliminating these unnecessary performance losses. The systems have generally been comprised of flow modulating valves or devices somewhere in a series of flow areas from source to sink. Many of the systems have been quite complex with many moving parts installed substantially internally within the engine and thus have been relatively inaccessible for inspection, adjustment or servicing. Many of these complex systems are also subject to reliability problems, such as binding or jamming, especially since they must often operate in hot and inaccessible areas which preclude or make difficult part lubrication or servicing.
It is therefore, an object of the present invention to provide an improved modulated cooling system for a gas turbine engine.
It is another object of the present invention to provide an improved cooling system for a gas turbine engine that includes a modulating system with an external actuator for easy access and service.
It is another object of the present invention to provide an improved cooling system for a gas turbine engine with cooling flow modulation using a structurally uncomplicated configuration that avoids excessive pressure losses.
These and other objects and features of the invention will become more readily apparent upon reference to the following description.